1. Technical Field
The present invention relates to a fuel vapor control system and the method thereof for automobile fuel tank and more specifically to an opening and closing control system and the method of a fuel passage communicating an upper space of a fuel tank and a canister.
2. Related Prior Arts
Commonly, in an automobile there is provided with a pressure control valve (PCV) in a fuel vapor passage which communicates an upper space of a fuel tank to a canister. The pressure control valve is opened or closed by the control of an electronic control unit. The control valve is controlled such that while the engine is in operation the fuel vapor passage is opened so as to prevent an increase of pressure within the fuel tank and while the engine is stopped the fuel vapor passage is closed so as to prevent an outflow of fuel vapor into atmospheric air.
That is to say, in the prior art when the pressure becomes higher than a specified value during engine operation the pressure control valve opens the fuel vapor passage and the fuel vapor filled in the upper space of the fuel tank is adsorbed into the canister through the fuel passage. When the engine is stopped for fueling, the pressure control valve closes the vapor passage and the fuel vapor is blocked to flow out of the vehicle through the canister. Accordingly, then an automatic stop of the fuel nozzle is operated to stop fueling.
However, in the abovementioned prior art, in case where the engine is inadvertently not stopped on fueling, the pressure control valve is opened when the pressure in the upper space of the fuel tank reaches a specified value. At this time the automatic stop of the fuel nozzle is not operated to stop fueling automatically. As a result, fuel is filled up in the fuel tank and eventually excessive fuel flows outside from the canister through the fuel vapor passage.
In order to prevent this, as disclosed in Japanese Patent Application Laid Open Nos. Jitsu-Kai-Hei 5-6144, Jitsu-Kai-Hei 5-6455 and Toku-Kai-Hei 5-10215, there is such a technique that the pressure control valve is closed when a fueling sensor, a fueling switch and the like detect an insertion of a fuel nozzle.
However, this technique needs an additional fueling sensor or switch to be installed on the vehicle and consequently the system becomes complicated.